The short-chain alcohol dehydrogenases (SCADs) are a diverse family of oxidoreductase enzymes. SCAD family members are involved in all aspects of cell biochemistry and physiology, including metabolism of sugar, synthesis or degradation of fatty acids, and synthesis or degradation of glucocorticoids, estrogens, androgens, and prostaglandins E.sub.2 and F2.alpha., SCADs are found in bacteria, plants, invertebrates, and vertebrates. Alignment of the different family members reveals large homologous regions and clustered similarities indicating sites of structural and functional importance. Some of these sites are associated with a type of coenzyme-binding domain, but similarity between family members extends beyond this domain. Family members typically show only about 15% to 30% identity between enzyme pairs. Over one third of the conserved residues are glycine residues, showing the importance of conformational and spatial restrictions. (Baker, M. E. (1995) Biochem. J. 309: 1029-1030; and Jomvall, H. et al. (1995) Biochemistry 34: 6003-6013.) SCAD family members show different subcellular distributions. For example, 2,4-dienoyl-CoA reductase is located in the mitochondria, whereas retinol dehydrogenase is located in microsomes.
The SCAD family can be divided into two groups based on the arrangement of two conserved structural motifs. The first group contains a highly conserved pentapeptide, containing a tyrosine and a lysine, separated by any three amino acid residues, at about residue 150 in a 250-residue dehydrogenase. The tyrosine and lysine residues, which are absolutely conserved within this group, are likely to be important in catalysis. Support for the importance of these two residues comes from mutagenesis studies with Drosophila alcohol dehydrogenase, human 15-hydroxyprostaglandin dehydrogenase, and human 11.beta.-hydroxysteroid and 17.beta.-hydroxysteroid dehydrogenases. (Baker, supra.) The AMP-binding domain at the N-terminus, which consists of a hydrophobic pocket containing three glycine residues in a seven amino acid sequence, is also highly conserved in this group. (Baker, supra.)
The second group lacks either the tyrosine or the lysine in the pentapeptide motif. For example, the tyrosine residue is replaced by a methionine in E. coli enoyl-acyl-carrier protein (EnvM), by serine in rat and human 2,4-dienoyl-CoA reductases, and by valine in S. cerevisiae sporulation specific protein (SPX19). Some members of this group also have differences in the AMP-binding domain, including an insertion of two residues and poor conservation of the second and third glycine residues. These changes do not seem to affect the enoyl-CoA reductase activity of the proteins, though in the case of EnvM NAD.sup.+ and substrate must bind simultaneously. (Baker, supra.)
The members of the SCAD family share a common function, utilizing NAD.sup.+ or NADP as a cofactor in oxidation-reduction reactions, but differ in their substrate specificity. For example, 17-.beta.-hydroxysteroid dehydrogenase interconverts estrone and estradiol, and androstenedione and testosterone. 2,4-dienoyl-CoA reductase participates in the metabolism of unsaturated fatty acids, and 15-hydroxyprostaglandin dehydrogenase is the main enzyme in prostaglandin degradation. Retinol dehydrogenase catalyzes the primary rate limiting step in retinoic acid synthesis, and 11 -cis-retinol dehydrogenase catalyzes the final step in the biosynthesis of 11 -cis-retinaldehyde, the universal chromophore of visual pigments.
SCAD involvement in fatty acid and steroid metabolism implicates members of the SCAD family in a variety of disorders. Steroid dehydrogenases, such as the hydroxysteroid dehydrogenases, are involved in hypertension, fertility, and cancer. (Duax, W. L. and Ghosh, D. (1997) Steroids 62: 95-100.) Reduction in 2,4-dienoyl-CoA reductase activity has been associated with hyperlysinemia and hypocarnitinemia. (Roe, C. R. et al. (1990) J. Clin. Invest. 85: 1703-1707.) Retinoic acid, a regulator of differentiation and apoptosis, has been shown to down-regulate genes involved in cell proliferation and inflammation. (Chai, X. et al. (1995) J. Biol. Chem. 270: 3900-3904.)
The discovery of new human SCAD family molecules and the polynucleotides encoding them satisfies a need in the art by providing new compositions which are useful in the diagnosis, treatment, and prevention of disorders associated with proliferation, inflammation, and fatty acid and steroid metabolism.